DEXA Anatomy & Physiology of Bone Structure 3 — Questions and Answers
Question 1: Peak bone mass in humans is typically achieved at approximately what age?
- Age 10–15
- Age 25–30 (Correct answer)
- Age 45–50
- Age 60–65
Correct answer: Age 25–30
Peak bone mass is generally reached between ages 25 and 30, after which bone density gradually declines.
Question 2: Which vertebral region is most commonly evaluated by DEXA for osteoporosis screening in the axial skeleton?
- Cervical (C1–C7)
- Thoracic (T1–T12)
- Lumbar (L1–L4) (Correct answer)
- Sacral (S1–S5)
Correct answer: Lumbar (L1–L4)
The lumbar spine (L1–L4) is the standard axial site evaluated by DEXA because it contains predominantly trabecular bone sensitive to metabolic changes.
Question 3: Endochondral ossification is the process by which:
- Flat bones form directly from mesenchymal tissue
- Long bones develop by replacing a cartilage template with bone (Correct answer)
- Bone marrow converts to cortical bone
- Osteoclasts remodel existing cortical bone
Correct answer: Long bones develop by replacing a cartilage template with bone
Endochondral ossification is the developmental process in which a hyaline cartilage model is gradually replaced by mineralized bone to form long bones.
Question 4: The epiphyseal growth plate (physis) is composed primarily of which tissue?
- Fibrous connective tissue
- Hyaline cartilage (Correct answer)
- Compact bone
- Dense elastic tissue
Correct answer: Hyaline cartilage
The growth plate is made of hyaline cartilage and is responsible for longitudinal bone growth in children until it ossifies at skeletal maturity.
Question 5: Which of the following best defines 'bone mineral density' (BMD) as measured by DEXA?
- The total volume of cortical bone in grams
- Bone mineral content divided by the projected scan area (g/cm²) (Correct answer)
- The ratio of trabecular to cortical bone
- Serum calcium level multiplied by bone volume
Correct answer: Bone mineral content divided by the projected scan area (g/cm²)
DEXA-derived BMD is calculated as bone mineral content (grams) divided by the two-dimensional projected scan area (cm²), yielding an areal density in g/cm².
Question 6: Osteocalcin is a protein produced by osteoblasts that serves as a biomarker of:
- Bone resorption
- Bone formation (Correct answer)
- Cartilage synthesis
- Calcium absorption
Correct answer: Bone formation
Osteocalcin is a non-collagenous protein secreted by osteoblasts during matrix synthesis and is used clinically as a marker of bone formation activity.
Question 7: Which type of collagen predominates in bone extracellular matrix and provides tensile strength?
- Type II collagen
- Type III collagen
- Type I collagen (Correct answer)
- Type IV collagen
Correct answer: Type I collagen
Type I collagen forms the organic scaffold of bone matrix and provides the tensile strength that complements the compressive strength of hydroxyapatite.
DEXA Anatomy & Physiology of Bone Structure 3
Peak bone mass in humans is typically achieved at approximately what age?